Interpretive Summary: Although corn gluten meal has shown promise as an early-season pre-emergent organic herbicide in sweet onion production, uncontrolled weeds can cause serious yield reductions by the end of the growing season. Research was conducted in southeast Oklahoma to determine the effectiveness of Matran EC (50% clove oil) as an organic post-emergent broadleaf herbicide. Intermediate day, sweet onion cvs. 'Candy' and 'Cimarron' were transplanted into 2 rows per 10 ft-long by 6 ft-wide raised beds. The experiment included 6 weed control treatments (2 application rates, 2 hand-weeding levels, an untreated weedy-check and an untreated weed-free) with 4 replications. Matran was applied at two rates, 5 and 7% v/v with BioLink (30% Yucca and 10% Garlic extract), 0.25% v/v, as an adjuvant, over the top of the onions. The two weed control treatments within each application rate (5 and 7% v/v) involved no hand-weeding, where the uncontrolled weeds were allowed to grow, or a season-long hand-weeding, where all weeds were removed. Applications of 5 and 7% rates of Matran EC provided poor (60% or less) broadleaf weed control at 2 days after treatment (DAT) and less than 20% by 18 DAT. Visual injury ratings for the two varieties were not different, but the yield response for the onion cultivars varied depending on weed control treatment. Although Matran did not cause severe visual crop injury or reduce onion plant populations, onion yields were reduced, indicating that caution should be taken when applying Matran as a broadcast over-the-top post-emergent organic herbicide with onions.

Technical Abstract:
Weed competition can cause serious yield reductions if not controlled throughout the growing season. Corn gluten meal can provide early season control, but additional organic herbicides need to be evaluated for mid to late season weed control. Research was conducted in southeast Oklahoma to determine the effectiveness of Matran EC (50% clove oil) as an organic post-emergent broadleaf herbicide. Intermediate day, sweet onion cvs. 'Candy' and 'Cimarron' were transplanted into 2 rows per 10 ft-long by 6 ft-wide raised beds. The experiment included 6 weed control treatments (2 application rates, 2 hand-weeding levels, an untreated weedy-check and an untreated weed-free) with 4 replications. Matran was applied at two rates, 5 and 7% v/v with BioLink (30% Yucca and 10% Garlic extract), 0.25% v/v, as an adjuvant, over the top of the onions. The two weed control treatments within each application rate (5 and 7% v/v) involved no hand-weeding, where the uncontrolled weeds were allowed to grow, or a season-long hand-weeding, where all weeds were removed. Applications of 5 and 7% rates of Matran provided poor (60% or less) broadleaf weed control at 2 days after treatment (DAT) and less than 20% by 18 DAT. Visual injury ratings for the two varieties were not different, but the yield response for the onion cultivars varied depending on weed control treatment. Although Matran did not cause severe visual crop injury or reduce onion plant populations, onion yields were reduced, indicating that caution should be taken when applying Matran as a broadcast over-the-top post-emergent organic herbicide with onions.